The present invention relates in general to battery power management in an automotive vehicle, and, more specifically, to avoiding depletion of a vehicle battery when a vehicle is parked that would result from an electronic module failing to properly enter a sleep state.
A typical automotive electrical system relies on a storage battery for starting an internal combustion engine (and/or closing the high voltage contactors for a hybrid vehicle) and for powering electrical accessories when the engine is not running. Many modern electronic vehicle systems operate continuously even when the vehicle is in a parked, unattended state when the battery is the only available power source. Some electronic modules that must be powered at all times include those that perform functional operations while parked (e.g., antitheft systems and remote entry systems) and those that just need a reduced amount of power to maintain memory contents or monitor/measure various conditions or electrical communication signals (e.g., in a sleep mode). Other modules may continue to operate for a specified time after the driver shuts off the vehicle, but can be powered off after the specified time (e.g., courtesy lighting).
Since a vehicle may remain parked for long periods of time, it is important to limit battery drain so that a sufficient battery state-of-charge is still available to activate the vehicle (e.g., start the engine or close the contactor) when the user returns. Therefore, the vehicle manufacturer specifies limits for the current drawn by various modules under each of the conditions which may arise. In particular, quiescent current limits are set for the modules which apply during times that the vehicle ignition switch has been OFF for a specified time and there has been no user activity. The sum of all the quiescent currents is sufficiently low to extend the ability to activate the vehicle for a sufficiently long time. Nevertheless, the potential remains for the battery to become depleted and unable to start the engine/activate the hybrid after some period of time.
In the event of a dead battery which occurs even though the time that the vehicle sat idle was shorter than the usual time that can be handled by a healthy battery, it is common for the battery to be replaced on the assumption that the battery is defective. Furthermore, customer satisfaction is negatively impacted. However, a dead battery may sometimes be caused by software glitches which resulted in a failure to reduce the battery drain down to the quiescent levels. For example, if one or more of electronic modules are awake during times when they should have entered a sleep mode, this could lead to a prematurely dead battery. The software glitches may not represent a permanent failure, and they may be difficult to detect because the software operation may fully recover after the next ignition cycle. Therefore, the battery may be replaced unnecessarily.
It is known to monitor the state-of-charge of the battery during a key-off condition. By measuring the actual battery state and comparing it to a low battery threshold, the prior art has attempted to avoid a dead battery by taking action to disconnect certain electrical loads after the battery capacity drops too low. Major disadvantages of such a system are that it reacts only after the battery capacity has already been negatively impacted and there is a loss of functionality when loads are disconnected.